A while back, I had acquired the Samyang 135mm F2 lens in Canon EOS mount for astrophotography, as it was available at a very good price. As this lens is very sharp even wide open, I felt I had to get the most out of it and consider narrowband imaging. While researching the filter choice, I had narrowed it down to either the Baader narrowband F2 filters or the Astronomik set (H-alpha, SII and OIII) in 1.25″. But I decided to go down the Astronomik route as this has always been the brand of astronomy filters I’ve used (other than the Baader U and UV/IR cut).One of the articles I had read found that the Astronomik H-alpha 12nm filter worked very well with an F/2 focal ratio telescope with even better contrast than the Baader 7nm and 35nm H-alpha filters. Now the things I’ve read online about the Astronomik filters suggests that these narrowband (12nm) filters are usable with optics up to F/3 without a significant reduction in performance. Astronomik do suggest contacting them if there is intention to use the filters for faster focal ratio systems.
Now the packaging of these narrowband filters, are unlike other Astronomik filters I’ve owned in the sense that they have included some important and interesting information; information which I have previously not found on the net. Hence I felt I had to post them here for others who may also be looking for narrowband filters for imaging with fast focal ratio systems.
So it looks like these filters will work well from f/2, and in fact the H-alpha filter will work well from f/1.8. That is very good news for those interested in using these filters with fast focal ratio optics. I’m pleased I bought these filters from Bernard at Modern Astronomy for a great price.
Now I just have to wait for the Geoptik Canon CCD adapter to arrive and for clear skies to try imaging with these filters, the Samyang 135mm F2 lens and ZWO ASI178MM-cooled; that will give me a ~650mm F2 imaging system.